(1) Field of the Invention
The invention is directed to a fire proof cable tray for carrying operating control tubes and instrumentation lines in refineries and chemical plants.
(2) Prior Art
There has long been a need for fire proofing operating control cables and instrumentation lines in oil refineries and chemical plants. Often in gasoline, fuel oil, and similar types of fires the temperature in the fire environment exceeded 2200.degree. F., with heat flux levels up to 26 Btu per square foot second. Because of the high flammability of products being stored and transported, protection against high temperature petroleum flash fires for extended periods of time is essential.
It is necessary that control cables and instrumentation lines must be made to withstand high temperatures, in the fires, for periods of time from 15 to 20minutes, or more, to permit an orderly shutdown to isolate the system and the fire extinguished with a minimum of damage to the control system.
Use of fire retardant coating systems for the control cables and instrumentation lines does not provide for adequate protection in hot fires, or for extended burning times. These cables and electrical lines are usually distributed throughout the plant and are generally all conducted through "trays", called cable trays, rather than through metal conduits. The cables and lines are simply laid out in these trays throughout the plant.
The advantage of the cable tray system is that repair work and adding new lines is often simplified, due to the easy access to the tray and its contents. A disadvantage is that, in the tray, the fire hazard is increased because of the number of cables set side by side, as well as the combustible debris which may collect in the suspended trays.
Other investigators have attempted to provide cable tray systems which provide fire protection for extended periods of time, i.e., in excess of 15 minutes. Most have concentrated on systems which merely stack layers of non-burning, insulating material either inside or outside the cable tray. For example, U.S. Pat. No. 4,064,359 discloses use of a two-layer blanket of fibers. The inner layer consists of glass fibers. The layer is coated with a halogen-containing coating containing 3 to 75% fire-proof fibers, such as asbestos.
U.S. Pat. No. 4,054,711 teaches a jacketing material having a polyester film, aluminum coating, asbestos paper, glass cloth and an outer layer of polyvinyl fluoride film. The fire-proof wrap material is used in a manner similar to the '359 patent. A cable coating which may be sprayed on is taught in U.S. Pat. No. 3,928,210. The slurry for spraying consists of non-combustible fibers in a water based resinous emulsion. U.S. Pat. No. 4,058,643 teaches use of an intumescent adhesive layer in fire retardant laminates. The inventor uses an intumescent adhesive to secure a polyethylene film to insulation batting. Two other patents of interest are U.S. Pat. No. 4,069,075 and U.S. Pat. No. 4,112,179.
It is an object of the invention to provide a cable tray construction to provide a fire protective insulating product capable of protecting control cables and instrumentation lines, contained therein, from external fire temperatures of at least 2200.degree. F. for a period of time in excess of 15 minutes.
It is a further object to provide an easily assembled, prefabricated cable tray capable of protecting the cables and lines secured therein from fire temperatures of 2200.degree. F. and higher for a period of time in excess of 15 minutes.
Another object is to provide the above cable tray which is adaptable for encasing cables and lines and also encasing structural beams in a refinery or plant.